Submarine experiments receive priority because the campaign plan calls for a large early force to defend widely scattered territories. These boats are an economical local defensive layer rather than substitutes for the battle fleet. Distributing them across the empire would force an attacker to account for undersea threats in several areas. Numerous limited-range craft can impose sea-denial risk even when they cannot provide global sea control.
Notable Point · 41:22-45:59
Building an early submarine force for distributed defense
Early submarine research supports a plan to distribute numerous defensive boats around Britain's scattered territories.